Photosensitive resin composition

ABSTRACT

A photosensitive resin composition according to the invention includes (A) a photosensitive resin, (B) an epoxy resin, (C) a photopolymerization initiator, and (D) a polymerizable unsaturated compound and/or a solvent, which photosensitive resin (A) is obtained by allowing an epoxy resin (a) to react with a compound (b) having one primary alcoholic hydroxyl group and one functional group selected from a carboxyl group and a secondary amino group per molecule and an unsaturated monobasic acid (c) to yield a reaction product (I) and allowing a saturated or unsaturated polybasic acid anhydride (d) to react with the reaction product (I). The photosensitive resin composition of the invention is used as a solder resist in printed circuit boards, can be satisfactorily developed in a dilute basic aqueous solution and can yield a cured film that is excellent in flexibility, water resistance, adhesion, solder heat resistance, electroless gold plating resistance and pressure cooker test (PCT) resistance.

TECHNICAL FIELD

The present invention relates to a photosensitive resin compositionwhich is used as a solder resist in printed circuit boards, can besatisfactorily developed in a dilute basic aqueous solution and canyield a cured film that is excellent in flexibility, water resistance,adhesion, solder heat resistance, electroless gold plating resistance,pressure cooker test (PCT) resistance and other properties.

BACKGROUND ART

To pattern resists on printed circuit boards, screen printing has beenconventionally used in many cases. However, a photosensitive resin thatcan be developed in a dilute basic solution as described in JapaneseExamined Patent Application Publication No. 1-54390 is now used toimprove productivity. This photosensitive resin is a novolak epoxy(meth)acrylate that has a carboxyl group in a side chain and is obtainedby allowing acrylic acid as an unsaturated monobasic acid to react witha novolak epoxy resin and allowing a saturated or unsaturated polybasicacid anhydride to react with the resulting hydroxyl group.

With increasing performances of electronic equipment, further downsizedsemiconductor packages have been launched in mass production. Forexample, ball grid arrays (BGAs), chip size packages (CSPS) and othersemiconductor packages are now commercially available.

These BGAs, CSPs and other parts are packed by heating a whole work withinfrared ray irradiation and reflowing solder to fix the parts. In thisprocedure, conventional solder resist films as described in JapaneseExamined Patent Application Publication No. 1-54390 may cause defectssuch as cracking due to heat shock. Demands are therefore made on resistfilms that have improved impact resistance, adhesion, solder heatresistance, electroless gold plating resistance, PCT resistance andother properties.

Japanese Unexamined Patent Application Publication No. 6-324490discloses a photosensitive resin which is obtained by allowing a novolakepoxy resin to react with dimethylolpropionic acid having two or morehydroxyl groups per molecule and acrylic acid as an unsaturatedmonobasic acid, and allowing the resulting product to react with asaturated or unsaturated polybasic acid anhydride. A cured product ofthis type of photosensitive resins may comprise hydroxyl groups inexcess and may therefore exhibit insufficient PCT resistance due to itsdeteriorated water resistance, since the amount of the added saturatedor unsaturated polybasic acid anhydride is less than that of thehydroxyl group of dimethylolpropionic acid, although it has excellentadhesion, solder heat resistance and electroless gold platingresistance. If the amount of saturated or unsaturated polybasic acidanhydride is increased to relatively decrease the amount of hydroxylgroups, the carboxyl groups are in excess to thereby cause insufficientPCT resistance in some cases. The use of an acid having two or morehydroxyl groups, such as dimethylolpropionic acid, induces excess of oneof the hydroxyl group and carboxyl group over another and is notpreferred.

Accordingly, an object of the present invention is to provide aphotosensitive resin composition which is used as a solder resist inprinted circuit boards, can be satisfactorily developed in a dilutebasic aqueous solution and can yield a cured film that is excellent inflexibility, water resistance, adhesion, solder heat resistance,electroless gold plating resistance and pressure cooker test (PCT)resistance.

SUMMARY OF THE INVENTION

After intensive investigations, the present inventors have solved theconventional problems.

Specifically, the present invention provides a photosensitive resincomposition comprising:

(A) a photosensitive resin;

(B) an epoxy resin;

(C) a photopolymerization initiator; and

(D) a polymerizable unsaturated compound and/or a solvent,

in which the photosensitive resin (A) is obtained by allowing an epoxyresin (a) to react with a compound (b) having one primary alcoholichydroxyl group and one functional group selected from a carboxyl groupand a secondary amino group per molecule, and an unsaturated monobasicacid (c) to yield a reaction product (I) and allowing a saturated orunsaturated polybasic acid anhydride (d) to react with the hydroxylgroup of the reaction product (I).

The photosensitive resin (A) in the photosensitive resin composition maybe obtained by allowing from 0.6 mole to 1.0 mole inclusive of thesaturated or unsaturated polybasic acid anhydride (d) to react with 1mole of the primary hydroxyl group of the reaction product (I).

In the photosensitive resin (A) of the photosensitive resin composition,0.8 to 1.2 equivalent weight in total of the compound (b) and theunsaturated monobasic acid (c) including 0.05 to 0.5 equivalent weightof the compound (b) may be allowed to react with 1 equivalent weight ofepoxy groups of the epoxy resin (a).

The photosensitive resin composition may comprise 1% to 50% by weight ofthe epoxy resin (B) based on the total weight of the composition.

The photosensitive resin composition may comprise 0.5% to 20% by weightof the photopolymerization initiator (C) based on the total weight ofthe composition.

Preferably, the photosensitive resin composition comprises 5% to 80% byweight of the polymerizable unsaturated compound and/or solvent (D)based on the total weight of the composition.

DISCLOSURE OF THE INVENTION

The present invention will be illustrated in further detail below.

Photosensitive resins (A) for use in the present invention are obtainedby allowing an epoxy resin (a) to react with a compound (b) having oneprimary alcoholic hydroxyl group and one functional group selected froma carboxyl group and a secondary amino group per molecule, and anunsaturated monobasic acid (c) to yield a reaction product (I) andallowing a saturated or unsaturated polybasic acid anhydride (d) toreact with the hydroxyl group of the reaction product (I).

Examples of the epoxy resin (a) include epoxy resins such as cresolnovolak epoxy resins, phenol novolak epoxy resins,dicyclopentadiene-phenol polyaddition epoxy resins and combinations ofthese resins. These novolak epoxy resins may be halogenated.

Part of such cresol novolak epoxy resins, phenol novolak epoxy resins,dicyclopentadiene-phenol polyaddition epoxy resins may be substitutedwith other epoxy resins within ranges not deteriorating the advantagesof the present invention. Such other epoxy resins include, but are notlimited to, bisphenol A epoxy resins, bisphenol F epoxy resins,hydrogenated bisphenol A epoxy resins, phenol-cresol co-condensationepoxy resins, bisphenol A novolak epoxy resins, bisphenol F novolakepoxy resins, triphenylolmethane epoxy resins, tetraphenylolethane epoxyresins and other epoxy resins prepared by allowing polyfunctionalphenols to react with epichlorohydrin, epoxy resins prepared by allowingpolyfunctional hydroxynaphthalenes to react with epichlorohydrin,silicone-modified epoxy resins, ε-caprolactone-modified epoxy resins,glycidylamine epoxy resins prepared by allowing epichlorohydrin to reactwith primary or secondary amines, triglycidyl isocyanate and otherheterocyclic epoxy resins.

Examples of the compound (b) having one primary alcoholic hydroxyl groupand one functional group selected from a carboxyl group and a secondaryamino group include glycolic acid, 16-hydroxyhexadecanoic acid and othercompounds each having a primary alcoholic hydroxyl group and a carboxylgroup; N-benzylethanolamine and other compounds each having a primaryalcoholic hydroxyl group and a secondary amino group, of which glycolicacid is typically preferred.

The alcoholic hydroxyl group of the compound (b) is a primary hydroxylgroup and has a higher reactivity with respect to the saturated orunsaturated polybasic acid anhydride (d) than a secondary hydroxylgroup. Such a secondary hydroxyl group is formed by the reaction of theepoxy group of the epoxy resin (a) with the carboxyl group or secondaryamino group of the compound (b) or with a carboxylic acid radical of theunsaturated monobasic acid (c). The saturated or unsaturated polybasicacid anhydride (d) therefore preferentially react with the primaryhydroxyl group rather than the secondary hydroxyl group. Thisphotosensitive resin (A) can yield a cured product that has crosslinkingpoints at longer intervals and is more flexible with higher developingproperty than cured products of conventional photosensitive resins asdescribed in Japanese Examined Patent Application Publication No.1-54390. Such conventional photosensitive resins are obtained byallowing a novolak epoxy resin to react with acrylic acid as anunsaturated monobasic acid and allowing a saturated or unsaturatedpolybasic acid anhydride to react with the formed secondary hydroxylgroup.

Based on the above mechanism, when the saturated or unsaturatedpolybasic acid anhydride is added in a number of moles higher than thatof the primary hydroxyl group, a primary hydroxyl group derivative inequivalent mole to that of the primary hydroxyl group is always formed,and the cured product of the resulting composition exhibits highflexibility. However, if the amount of the added saturated orunsaturated polybasic acid anhydride is excessively high (if it exceeds0.7 mole relative to 1 mole of the total hydroxyl group of the reactionproduct (I)), the cured product exhibits deteriorated PCT resistance.The amount of the saturated or unsaturated polybasic acid anhydride tobe added is preferably less than or equal to 0.7 mole, relative to 1mole of the total hydroxyl groups of the reaction product (I). Morepreferably, the amount is equal to or more than 0.6 mole and less thanor equal to 1.0 mole relative to 1 mole of the primary hydroxyl group ofthe reaction product (I). If the amount is less than 0.6 mole, thehydroxyl group becomes excessive to thereby deteriorate PCT resistanceand developing property.

The unsaturated monobasic acid (c) is a monobasic acid having onecarboxyl group and one or more polymerizable unsaturated bonds, of whichacrylic acid and methacrylic acid are preferred. Acrylic acid istypically preferred to yield high curability with active light orradiant rays. In addition, such unsaturated monobasic acids includecrotonic acid, cinnamic acid, sorbic acid, acrylic acid dimer,monomethyl maleate, monopropyl maleate, monobutyl maleate, andpolyfunctional carboxyl-group-containing acrylates or methacrylateswhich are reaction products of polyfunctional acrylates or methacrylateseach having one hydroxyl group and one or more acryloyl groups withdibasic acids among polybasic acid anhydrides mentioned below. Each ofthese unsaturated monobasic acids can be used in combination.

In the reaction among the epoxy compound (a), the compound (b) and theunsaturated monobasic acid (c), preferably about 0.8 to about 1.2equivalent weight, and more preferably about 0.9 to about 1.1 equivalentweight, of the total of the compound (b) and the unsaturated monobasicacid (c) is allowed to react with 1 equivalent weight of the epoxy groupof the epoxy compound (a). In this reaction, the amount of the compound(b) is preferably 0.05 to 0.5 equivalent weight relative to 1 equivalentweight of the epoxy group of the epoxy compound (a).

In the reaction, a diluent is preferably used. Such diluent include, butare not limited to, methyl ethyl ketone, cyclohexanone and otherketones; toluene, xylene, tetramethylbenzene and other aromatichydrocarbons; dipropylene glycol dimethyl ether, dipropylene glycoldiethyl ether and other glycol ethers; ethyl acetate, butyl cellosolveacetate, carbitol acetate and other esters; octane, decane and otheraliphatic hydrocarbons; petroleum ether, petroleum naphtha, hydrogenatedpetroleum naphtha, solvent naphtha and other petroleum solvents andother organic solvents, as well as carbitol (meth)acrylate,pentaerythritol tetra(meth)acrylate, trimethylolpropane (meth)acrylate,tris(hydroxyethyl) isocyanurate tri(meth)acrylate, dipentaerythritolhexa(meth)acrylate and other reactive monomers. In addition, a catalystis preferably used to accelerate the reaction. Such catalysts include,for example, triethylamine, benzyldimethylamine, methyltriethylammoniumchloride, benzyltrimethylammonium bromide, benzyltrimethylammoniumiodide, triphenylphosphine, triphenyl stibine, chromium octanoate andzirconium octanoate. The amount of the catalyst is preferably 0.01% to1% by weight relative to the weight of the reaction material mixture.The reaction is preferably performed at 60° C. to 150° C. for 5 to 60hours. Thus, the reaction product (I) can be obtained.

Preferred examples of the saturated or unsaturated polybasic acidanhydride (d) are maleic anhydride, succinic anhydride, itaconicanhydride, phthalic anhydride, tetrahydrophthalic anhydrous,hexahydrophthalic anhydride, endomethylenetetrahydrophthalic anhydride,methyltetrahydrophthalic anhydride, chlorendic anhydride and otherdibasic acid anhydrides; trimellitic anhydride, pyromellitic anhydride,benzophenonetetracarboxylic anhydride, biphenyltetracarboxylic anhydrideand other polybasic acid anhydrides. Among them, tetrahydrophthalicanhydride, succinic anhydride and hexahydrophthalic anhydride aretypically preferably used.

The reaction is preferably performed at 60° C. to 150° C. for 1 to 10hours.

The content of the photosensitive resin (A) in the composition of thepresent invention is preferably 10% to 80% by weight and more preferably15% to 60% by weight based on the total weight of the composition.

The epoxy resin (B) is a thermosetting component and has one or moreepoxy groups per molecule. Such epoxy resins include, for example,bisphenol A epoxy resins, bisphenol F epoxy resins, hydrogenatedbisphenol A epoxy resins, phenol novolak epoxy resins, cresol novolakepoxy resins, dicyclopentadiene-phenol novolak epoxy resins,phenol-cresol novolak co-condensation epoxy resins, bisphenol A novolakepoxy resins, bisphenol F novolak epoxy resins or halogenated epoxycompounds of these resins, triphenylolmethane epoxy resins,alkyl-substituted triphenylolmethane epoxy resins, tetraphenylolethaneepoxy resins and other epoxy resins obtained by allowing polyfunctionalphenols to react with epichlorohydrin, epoxy resins obtained by allowingpolyfunctional hydroxynaphthalenes to react with epichlorohydrin,silicone-modified epoxy resins, ε-caprolactone-modified epoxy resins,glycidylamine epoxy resins obtained by the reaction betweenepichlorohydrin and primary or secondary amines, triglycidyl isocyanateand other heterocyclic epoxy resins. Each of these epoxy resins (B) canbe used alone or in combination.

The epoxy resins (B) are used to improve properties as the solderresist, such as adhesion, heat resistance and plating resistance.

Each of the epoxy resins (B) is used alone or in combination as amixture, and the amount of the epoxy resins (B) in the composition ofthe present invention is preferably 1% to 50% by weight and morepreferably 3% to 45% by weight based on the total weight of thecomposition.

The epoxy resin (B) is preferably used in combination with an epoxycuring agent in order to further improve adhesion, chemical resistance,heat resistance and other properties. Such epoxy curing agents include,for example, imidazoles, amines, guanamines, polyamines, triazinederivatives, tertiary amines, polyphenols, organophosphines, phosphoniumsalts, quaternary ammonium salts, and photocationic polymerizationcatalysts. Examples of such epoxy curing agents are imidazoles such as2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole,2-phenylimidazole, 2-undecylimidazole, 2-heptadecylimidazole,1-benzyl-2-methylimidazole, 2-phenyl-4-methylimidazole,1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-phenylimidazole,1-cyanoethyl-2-undecylimidazole,2-phenyl-4,5-bis(hydroxymethyl)imidazole and 2-alkylformylimidazoles;guanamines such as acetoguanamine and benzoguanamine; amines such asdiaminodiphenylmethane, m-phenylenediamine, m-xylylenediamine,diaminodiphenyl sulfone, dicyandiamide, urea and urea derivatives;guanamines such as acetoguanamine and benzoguanamine; polyamines such asmelamine, polybasic hydrazide, or organic acid salts and/or epoxyadducts of these compounds, and boron trifluoride amine complex;triazine derivatives such as ethylamino-S-triazine,2,4-diamino-S-triazine, 2,4-diamino-S-triazine and2,4-diamino-6-xylyl-S-triazine; tertiary amines such as trimethylamine,triethanolamine, N,N-dimethyloctylamine, N-benzyldimethylamine,pyridine, N-methylmorpholine, hexa(N-methyl)melamine,2,4,6-tris(dimethylaminophenol) and tetramethylguanidine; polyphenolssuch as polyvinylphenol, polyvinylphenol bromides, phenol novolaks, andalkylphenol novolaks; organophosphines such as tributylphosphine,triphenylphosphine and tris-2-cyanoethylphosphine; phosphonium saltssuch as tri-n-butyl(2,5-dihydroxyphenyl)phosphonium bromide,hexadecyltributylphosphonium bromide and hexadecyltributylphosphoniumbromide; quaternary ammonium salts such as benzyltrimethylammoniumchloride, phenyltributylammonium chloride and other derivatives; as wellthe aforementioned saturated or unsaturated polybasic acid anhydrides,diphenyliodonium tetrafluoroborate, triphenylsulfoniumhexafluoroantimonate, 2,4,6-triphenylthiopyridinium hexafluorophosphate,iron-arene complexes and other photocationic polymerization catalysts;conventional curing agents or curing accelerators for use in thereaction of styrene-maleic acid resin. Each of these compounds can beused alone or in combination. The amount of the epoxy resin curing agentis preferably 0.01 to 25 parts by weight and more preferably 0.1 to 15parts by weight relative to 100 parts by weight of the epoxy resin (B).

The photopolymerization initiator (C) includes, for example, benzoins,acetophenones, anthraquinones, thioxanthones and benzophenones. Examplesof these compounds are benzoins such as benzoin and benzoin methylether, benzoin isopropyl ether and other benzoin derivatives;acetophenones such as acetophenone, 2,2-dimethoxy-2-phenylacetophenoneand other acetophenone derivatives; anthraquinones such as2-methylanthraquinone, 2-chloroanthraquinone, 2-ethylanthraquinone,2-t-butylanthraquinone, and other anthraquinone derivatives;thioxanthones such as thioxanthone, 2,4-dimethylthioxanthone and otherthioxanthone derivatives; benzophenones such as benzophenone,4-benzoyl-4′-methyldiphenyl sulfide, 4,4′-dichlorobenzophenone,N,N-dimethylaminobenzophenone and other benzophenone derivatives, aswell as 2,4,6-trimethylbenzoyldiphenylphosphine oxide. Each of thesecompounds can be used alone or in combination. The photopolymerizationinitiator (C) can be used in combination with one or more types ofphotosensitizers such as tertiary amines. Such tertiary amines include,for example, ethyl N,N-dimethylaminobenzoate, isoamylN,N-dimethylaminobenzoate, pentyl-4-dimethylaminobenzoate, triethylamineand triethanolamine.

Preferably, 2-ethyl-1-[4-(methylthio)phenyl]-2-morpholinolpropan-1-oneis used in combination with at least one selected from2,4-diethylthioxanthone, 4-benzoylthioxanthone and2-isopropylthioxanthone.

The amount of the photopolymerization initiator (C) is preferably 0.5%to 20% by weight and more preferably 1% to 10% by weight based on thetotal weight of the composition of the present invention.

As a diluent, the polymerizable unsaturated compound and/or solvent (D)can be used. This component is used in order to improve coatability whena curable and/or photosensitive resin composition with respect to activelight or radiant ray is used as a resist ink.

As such polymerizable unsaturated compounds, monomers that can be curedwith active light or radiant ray are preferred. Such monomers include,for example, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, isoamylacrylate, butoxyethyl acrylate, methoxypolyethylene glycol acrylate,ethoxypolyethylene glycol acrylate, melamine acrylate, phenoxyethylacrylate, phenoxypropyl acrylate, ethylene glycol diacrylate,dipropylene glycol diacrylate, poly(dipropylene glycol diacrylate),phenyl glycidyl ether acrylate-tolylene diisocyanate urethaneprepolymer, PO-modified bisphenol A diacrylate, N-pyrrolidone,N-acryloylmorpholine, N,N-dimethylacrylamide, N,N-diethylacrylamide,N,N-dimethylaminoethyl acrylate, N,N-dimethylaminopropyl acrylate,trimethylolpropane triacrylate, pentaerythritol triacrylate,pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, glyceroldiacrylate, isobornyl acrylate, dicyclopentenyloxyethyl acrylate, andmethacrylates corresponding to these acrylates. Each of thesepolymerizable unsaturated compounds can be used alone or in combination.

The solvents include, for example, ketones, aromatic hydrocarbons,carbitols and acetates. Examples of such solvents are ketones such asmethyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; aromatichydrocarbons such as toluene and xylene; carbitols such as ethylcellosolve, butyl cellosolve, carbitol and butyl carbitol; acetates suchas ethyl acetate, butyl acetate, cellosolve acetate, butyl cellosolveacetate and carbitol acetate. Each of these solvents can be used aloneor in combination.

Each of the polymerizable unsaturated compounds and/or solvents (D) canbe used alone or in combination as a mixture. The amount of thecomponent (D) is preferably from 5% to 80% by weight and more preferablyfrom 10% to 70% by weight based on the total weight of thephotosensitive resin composition of the present invention.

When the photosensitive resin composition of the present invention isused as a liquid resist ink, it may further comprise additives accordingto necessity. Such additives include, for example, silica, calciumcarbonate, barium sulfate, clay, talc and other inorganic fillers;phthalocyanine green, phthalocyanine blue, titanium oxide, carbon blackand other coloring pigments; defoaming agents; and leveling agents; aswell as hydroquinone, resorcinol, catechol, pyrogallol, hydroquinonemonomethyl ether, t-butylcatechol, phenothiazine and otherpolymerization inhibitors. The amount of these additives is preferably0% to 60% by weight and more preferably 5% to 40% by weight based on thetotal weight of the photosensitive resin composition of the presentinvention.

The photosensitive resin composition may further comprise copolymers ofethylenically unsaturated compounds, polyester resins and otherconventional binder resins; polyester (meth)acrylate, polyurethane(meth)acrylate, epoxy (meth)acrylate and other unsaturatedgroup-containing polymerizable oligomers, within ranges not adverselyaffecting the properties as a solder resist.

The photosensitive resin composition of the present invention isobtained by compounding the individual components preferably in theaforementioned proportions and homogeneously blending them using, forexample, a triple roll mill.

The photosensitive resin composition of the present invention is cured,for example, in the following manner and thereby yields a cured product.Specifically, the composition of the present invention is applied onto aprinted circuit board to a thickness of 10 to 160 μm by screen printing,spraying, roll coater coating, electrostatic painting, curtain coatingor another technique, the resulting film is dried at 60° C. to 110° C.,a negative film is brought into direct contact with the film or isplaced on the film without contact, the film is then irradiated withultraviolet rays, the unexposed portions of the film are then dissolvedand removed (developed) with a dilute basic aqueous solution (e.g., 0.5%to 2% sodium carbonate aqueous solution or sodium hydroxide aqueoussolution), and the film is further sufficiently cured by ultravioletrays irradiation and/or heating (e.g., heating at 100° C. to 200° C. for0.5 to 1.0 hour) to further improve the physical properties and therebyyields a cured film.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be illustrated in further detail withreference to several examples and comparative examples below. All partsand percentages are by weight unless otherwise specified.

SYNTHESIS EXAMPLE 1

Synthesis Example of Photosensitive Resin (A-1)

A total of 2100 parts (10 equivalent weight) of a cresol novolak epoxyresin (available from Tohto Kasei Co., Ltd. under the trade name ofEpotohto YDCN-704, softening point: 80° C., epoxy equivalent: 210), 576parts (8 moles) of acrylic acid, 152 parts (2 moles) of glycolic acid,2.8 parts of methylhydroquinone and 2097 parts of carbitol acetate weremixed, the resulting mixture was heated to 90° C. and thereby yielded ahomogenous solution. Thereafter, the resulting solution was mixed with14.1 parts of triphenylphosphine, was heated to 100° C., was allowed toreact for about 40 hours and thereby yielded a reaction product havingan acid value of 0.5 KOH-mg/g (hydroxyl group 12 equivalent weight). Thereaction product was mixed with 301 parts (1.98 moles; the ratio oftetrahydrophthalic anhydride to 1 mole of primary hydroxyl group of theresulting reaction product (I) was 0.99 mole) of tetrahydrophthalicanhydride, was heated to 95° C., was allowed to react for about 6 hoursand thereby yielded a photosensitive resin (A-1) having an acid value insolids of 36 KOH-mg/g and a solid concentration of 60%. H-NMR and¹³C-NMR analyses revealed that the primary hydroxyl group disappearedfrom the photosensitive resin (A-1).

SYNTHESIS EXAMPLES 2 TO 8

A series of photosensitive resins (A-2), (A-3), (A-4), (A-5), (B-1),(B-2) and (B-3) each having a solid concentration of 60% were obtainedin the same manner as in Synthesis Example 1, except that the chargedamounts of the cresol novolak epoxy resin, acrylic acid, glycolic acid,methylhydroquinone, carbitol acetate, triphenylphosphine andtetrahydrophthalic anhydride in Synthesis Example 1 were changed asshown in Table 1 or 2.

SYNTHESIS EXAMPLE 9

A total of 2200 parts (10 equivalent weight) of cresol novolak epoxyresin (available from Nippon Kayaku Co., Ltd. under the trade name ofEOCN-104S, softening point: 92° C., epoxy equivalent: 220), 134 parts (1mole) of dimethylolpropionic acid, 648.5 parts (9 moles) of acrylicacid, 4.6 parts of methylhydroquinone, 1131 parts of carbitol acetateand 484.9 parts of solvent naphtha were mixed, the resulting mixture washeated to 90° C. and was stirred to thereby dissolve the resultingreaction mixture. The reaction mixture was cooled to 60° C., was mixedwith 13.8 parts of triphenylphosphine, was heated to 100° C., wasallowed to react for about 32 hours and thereby yielded a reactionproduct having an acid value of 0.5 mg-KOH/g (hydroxyl group: 12equivalent weight). The reaction product was then mixed with 702 parts(4.6 moles) of tetrahydrophthalic anhydride, 264.7 parts of carbitolacetate and 113.5 parts of solvent naphtha, was heated to 95° C., wasallowed to react for about 6 hours, was cooled and thereby yielded aphotosensitive resin (B-4) having an acid value of solid contents of 70mg-KOH/g and a solid concentration of 65%.

TABLE 1 Synthesis Example 2 3 4 5 Cresol novolac epoxy 2100 2100 21002100 resin (10 eq) (10 eq) (10 eq) (10 eq) Acrylic acid  504  504  432 525.6  (7 mol)  (7 mol)  (6 mol)  (7.3 mol) Glycolic acid  228  228 304  205.2  (3 mol)  (3 mol)  (4 mol)  (2.7 mol) Dimethylolpropionic  0   0   0   0 acid  (0 mol)  (0 mol)  (0 mol)  (0 mol)Methylhydroquinone   2.8   2.8   2.8   2.8 Carbitol acetate 2153 22002206 2202 Triphenylphosphine  14.1  14.1  14.1  14.1 Tetrahydrophthalic 380  451  456  456 anhydride  (2.5 mol)  (2.97 mol)  (3.0 mol)  (3.0mol) Ratio of tetra-   0.83   0.99   0.75   1.11 hydrophthalic anhydrideto primary hydroxyl group of (I) Acid value in solids  44  51  51  51(KOH-mg/g) Photosensitive resin A-2 A-3 A-4 A-5

TABLE 2 Synthesis Example 6 7 8 9 Cresol novolac epoxy 2100 2100 21002200 resin (10 eq) (10 eq) (10 eq) (10 eq) Acrylic acid  504  720  720 648.5  (7 mol) (10 mol) (10 mol)  (9 mol) Glycolic acid   0   0   0   0 (0 mol)  (0 mol)  (0 mol)  (0 mol) Dimethylolpropionic  402   0   0 134 acid  (3 mol)  (0 mol)  (0 mol)  (1 mol) Methylhydroquinone   2.8  2.8   2.8   4.6 Carbitol acetate 2257 2691 1931 1395.7Triphenylphosphine  14.1  14.1  14.1  13.8 Tetrahydrophthalic  380 1216 76  702.3 anhydride  (2.5 mol)  (8.0 mol)  (0.5 mol)  (4.6 mol) Ratioof tetra-   0.42 — —   0.225 hydrophthalic anhydride to primary hydroxylgroup of (I) Acid value in solids  42  111  10  70 (KOH-mg/g)Photosensitive resin B-1 B-2 B-3 B-4

Using each of the photosensitive resins obtained in the synthesisexamples, ink compositions (i) and (ii) were compounded and were kneadedin a triple roll mill, respectively, and 500 g of the ink composition(i) and 128 g of the ink composition (ii) were then mixed with eachother and thereby yielded a photosensitive resin composition (iii). Thephotosensitive resin composition (iii) was applied onto a buffed andpatterned printed circuit board to a thickness on wet basis of 40 to 80μm by screen printing using a 100-mesh polyester screen. The resultingfilm was dried using a hot air dryer at 85° C. for a predetermined time,the dried film was brought into intimate contact with a negative filmcarrying a patterned resist and was then irradiated with ultravioletrays at a dose of 350 mJ/cm² using an UV aligner. Next, the negativefilm was removed off, the unexposed portions of the coated film weredissolved and removed by development with 1% sodium carbonate aqueoussolution at a spray pressure of 2.0 kg/cm² for 60 seconds, anddeveloping property was determined. The resulting film was then heatedand cured using a hot air dryer at 150° C. for 20 minutes and therebyyielded test pieces for the following adhesion, solder heat resistance,gold plating resistance, PCT resistance and flexibility tests. Theresults of these tests are shown in Tables 4 and 5. The photosensitiveresin compositions using the resins obtained in Synthesis Examples 1 to5 were evaluated as Examples 1 to 5, respectively. The photosensitiveresin compositions using the resins obtained in Synthesis Examples 6 to9 were evaluated as Comparative Examples 1 to 4, respectively.

TABLE 3 Component Name Amount Ink Composition (i) Photosensitive resin308.0 parts  Photopolymerization Irgacure 907 24.0 parts initiatorKayacure DETX-S  1.0 part  Diluent Carbitol acetate 10.0 parts Solvesso150 10.0 parts DPE-6A 20.0 parts Others Fuselex 109.4 parts  Aerosil 38010.0 parts Phthalocyanine green  3.6 parts Dicyandiamide  2.0 partsTotal 500.0 parts  Ink Composition (ii) Thermosetting YDCN-704  9.0parts component TEPIC 37.0 parts Diluent LIGHT-ACRYLATE TMP-A 18.0 partsCarbitol acetate 18.0 parts Solvesso 150  9.0 parts Others Bariumsulfate 37.0 parts Total 128.0 parts 

Developing Property

In the above procedure, the films were dried for 20 minutes, 40 minutes,60 minutes, 80 minutes and 100 minutes, respectively, and the resultingfilms were visually inspected using a magnifier to thereby determine thedeveloping property according to the following criteria: Good: The inkwas completely removed during development and the film wassatisfactorily developed. Poor: The film had any undeveloped portionafter development.

Adhesion

According to the method specified in Japanese Industrial Standards (JIS)D 0202, a cured film under test was scribed to form crosscut sections. Acellophane adhesive tape was applied to the crosscut film and thenpeeled off therefrom, and the film was visually observed to inspectwhether or not the crosscut sections were peeled off. The adhesion ofthe film was determined according to the following criteria: Good: Nopeeling was observed. Fair: A few of crosscut sections were peeped off.Poor: The film was peeled off.

Solder Heat Resistance

A test piece was dipped in a bath of molten solder at 260° C. for 10minutes, this procedure was repeated three times as a total, and thetest piece was then visually inspected according to the method specifiedin JIS C 6481. The solder heat resistance was then determined accordingto the following criteria: Good: The cured film showed no change inappearance. Fair: The cured film changed in color. Poor: The cured filmshowed lifting, peeling or solder wicking or webbing.

Electroless Gold Plating Resistance

A test piece was subjected to the following pretreatment. Specifically,it was subjected to dipping in an acidic degreasing agent solution at30° C., dipping in water for rinsing, soft etching, dipping in water forrinsing, mixing with a catalyst (dipping in a nickel plating catalystsolution at 30° C. for 7 minutes) and dipping in water for rinsing inthis order, followed by electroless nickel plating. In the electrolessnickel plating process, the test piece was dipped in a nickel platingsolution pH 4.6 at 85° C. for 20 minutes, was then dipped in an acid (10vol. % sulfuric acid aqueous solution) at room temperature for 1 minuteand was dipped in water for rinsing, followed by electroless goldplating. In the electroless gold plating process, the test piece wasdipped in a gold plating solution (3 vol. % potassium cyanoaurateaqueous solution, pH 6) at 95° C. for 10 minutes, was dipped in waterfor rinsing, was dipped in hot water at 60° C. for rinsing, was furthersufficiently rinsed with water, was sufficiently drained and was driedin this order to thereby complete the electroless gold plating process.The test piece was then visually inspected, was subjected to a peelingtest using a cellophane adhesive tape and the resulting film wasobserved. The electroless gold plating resistance was determinedaccording to the following criteria: Good: The test piece showed nochange in appearance and no resist peeling. Fair: The test piece showedno change in appearance but showed slight resist peeling. Poor: The testpiece showed resist floating and plate wicking or webbing, and theresist significantly peeled off in the peeling test.

PCT Test

A test piece was left stand at 121° C. in an atmosphere of saturatedvapor at 2 atm for 100 hours, and the resulting film was visuallyinspected to determine the PCT resistance according to the followingcriteria: Good: The film was neither blistered nor peeled. Poor: Thefilm was blistered and/or peeled.

Flexibility Test

A test piece was subjected to a flexibility test according to the methodspecified in JIS K5400 using an Erichsen tester specified in the methodA of JIS B7729. Specifically, the photosensitive resin composition (iii)was applied onto a bonderized plate, was dried, was irradiated withlight or rays, was developed, was heated in this order, and a rigid ballwas pushed from the back side of the resulting test piece to therebydeform the test piece, and the distance covered by the pushed rigid balluntil the film was cracked or peeled off was determined. The flexibilitywas then determined according to the following criteria: Good: The filmwas neither cracked nor peeled off even the rigid ball was pushed 3 mmor more. Fair: The film was cracked and peeled off when the rigid ballwas pushed equal to or more than 3 mm and less than 4 mm. Poor: The filmwas cracked and peeled off when the rigid ball was pushed less than 3mm.

In the composition of Table 3, Irgacure 907 is2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one availablefrom Ciba Geigy Ltd., Kayacure DETX-S is 2,4-diethylthioxanthoneavailable from Nippon Kayaku Co., Ltd., Solvesso 150 is solvent naphthaavailable from ExxonMobil Chemical, LIGHT-ACRYLATE DPE-6A is a mixtureof dipentaerythritol hexaacrylate and dipentaerythritol pentaacrylateavailable from Kyoeisha Chemical Co., Ltd., Fuselex is a fused silicaavailable from Tatsumori Co., Aerosil 380 is anhydrous silica availablefrom Nippon Aerosil Co., Ltd., YDCN-704 is a o-cresol novolak epoxyresin available from Tohto Kasei Co., Ltd., TEPIC is triglycidyl etherisocyanurate available from Nissan Chemical Industries, Ltd., andLIGHT-ACRYLATE TMP-A is trimethylolpropane triacrylate available fromKyoeisha Chemical Co., Ltd.

TABLE 4 Photo- sensitive Time (min.) of drying the coating at 85° C.resin 20 40 60 80 100 Ex. 1 A-1 Good Good Poor Poor Poor Ex. 2 A-2 GoodGood Good Poor Poor Ex. 3 A-3 Good Good Good Good Good Ex. 4 A-4 GoodGood Good Good Good Ex. 5 A-5 Good Good Good Good Good Com. Ex. 1 B-1Good Good Poor Poor Poor Com. Ex. 2 B-2 Good Poor Poor Poor Poor Com.Ex. 3 B-3 Poor Poor Poor Poor Poor Com. Ex. 4 B-4 Good Good Poor PoorPoor

TABLE 5 Tests Photo- Solder Electroless sensitive heat gold plating PCTresin Adhesion resistance resistance resistance Flexibility Ex. 1 A-1Good Good Good Good Good Ex. 2 A-2 Good Good Good Good Good Ex. 3 A-3Good Good Good Good Good Ex. 4 A-4 Good Good Good Good Good Ex. 5 A-5Good Good Good Good Good Com. Ex. 1 B-1 Good Good Fair Poor Good Com.Ex. 2 B-2 Fair Poor Poor Poor Poor Com. Ex. 3 B-3 Poor Poor Poor PoorPoor Com. Ex. 4 B-4 Good Good Poor Poor Fair The results are of coatingsthat were dried at 85° C. for 20 minutes and were then cured under theaforementioned conditions.

The results in Tables 4 and 5 show that the photosensitive resincompositions of the present invention can be satisfactorily developed ina dilute basic aqueous solution and can be developed even when thesolvent is removed by long-term drying and can yield cured products thathave excellent adhesion, solder heat resistance, electroless goldplating resistance, PCT resistance and flexibility.

REFERENCE EXAMPLE

To verify whether or not an acid anhydride is preferentially added to aprimary hydroxyl group, a reference test was performed using a compoundhaving a primary hydroxyl group and a compound having a secondaryhydroxyl group.

Into 152 parts (1 mole) of tetrahydrophthalic anhydride heated at 95°C., 130 parts (1 mole) of 1-octanol as the compound having a primaryhydroxyl group and 130 parts (1 mole) of 2-octanol as the compoundhaving a secondary hydroxyl group were added, and the resulting mixturewas allowed to react at 100° C. for about 3 hours. IR analysis of theresulting reaction product revealed that the absorption of the acidanhydride disappeared. The reaction rate of the reaction product wasdetermined by Gel permeation chromatography (GPC) and revealed that theaddition rate of tetrahydrophthalic anhydride was 99% or more threehours into the reaction. In addition, H-NMR and ¹³C-NMR analyses on thereaction product revealed that the primary hydroxyl group disappearedand the secondary hydroxyl group did not disappeared. These results showthat the acid anhydride is preferentially added to the primary hydroxylgroup.

INDUSTRIAL APPLICABILITY

In solder resist patterning in which a film is selectively irradiatedwith ultraviolet rays through a patterned film and the unexposedportions of the film are removed by development, the photosensitiveresin composition of the present invention is resistant to developingsolutions in exposed portions and can yield a cured product that isexcellent in electroless gold plating resistance and have satisfactoryadhesion, solder heat resistance, PCT resistance and other properties.The photosensitive resin composition is therefore specifically suitableas a photosensitive resin composition for use as a liquid solder resist.

The present invention can therefore provide a photosensitive resincomposition which is used as a solder resist in printed circuit boards,can be satisfactorily developed in a dilute basic aqueous solution andcan yield a cured film that is excellent in flexibility, waterresistance, adhesion, solder heat resistance, electroless gold platingresistance and pressure cooker test (PCT) resistance.

What is claimed is:
 1. A photosensitive resin composition comprising:(A) a photosensitive resin; (B) an epoxy resin; (C) aphotopolymerization initiator; and (D) a polymerizable unsaturatedcompound and/or a solvent, wherein the photosensitive resin (A) isobtained by allowing an epoxy resin (a) to react with a compound (b)having only one primary alcoholic hydroxyl group and one functionalgroup selected from a carboxyl group and a secondary amino group permolecule and an unsaturated monobasic acid (c) to yield a reactionproduct (I) and allowing a saturated or unsaturated polybasic acidanhydride (d) to react with the hydroxyl group of the reaction product(I).
 2. The photosensitive resin composition according to claim 1,wherein the photosensitive resin (A) is obtained by allowing from 0.6mole to 1.0 mole inclusive of the saturated or unsaturated polybasicacid anhydride (d) to react with 1 mole of the primary hydroxyl group ofthe reaction product (I).
 3. The photosensitive resin compositionaccording to claim 1, wherein 0.8 to 1.2 equivalent weight in total ofthe compound (b) and the unsaturated monobasic acid (c) including 0.05to 0.5 equivalent weight of the compound (b) is allowed to react with 1equivalent weight of epoxy groups of the epoxy resin (a) in thephotosensitive resin (A).
 4. The photosensitive resin compositionaccording to claim 1, wherein the composition comprises 1% to 50% byweight of the epoxy resin (B) based on the total weight of thecomposition.
 5. The photosensitive resin composition according to claim1, wherein the composition comprises 0.5% to 20% by weight of thephotopolymerization initiator (C) based on the total weight of thecomposition.
 6. The photosensitive resin composition according to claim1, wherein the composition comprises 5% to 80% by weight of thepolymerizable unsaturated compound and/or solvent (D) based on the totalweight of the composition.
 7. The photosensitive resin compositionaccording to claim 2, wherein 0.8 to 1.2 equivalent weight in total ofthe compound (b) and the unsaturated monobasic acid (c) including 0.05to 0.5 equivalent weight of the compound (b) is allowed to react with 1equivalent weight of epoxy groups of the epoxy resin (a) in thephotosensitive resin (A).
 8. The photosensitive resin compositionaccording to claim 2, wherein the composition comprises 1% to 50% byweight of the epoxy resin (B) based on the total weight of thecomposition.
 9. The photosensitive resin composition according to claim2, wherein the composition comprises 0.5% to 20% by weight of thephotopolymerization initiator (C) based on the total weight of thecomposition.
 10. The photosensitive resin composition according to claim2, wherein the composition comprises 5% to 80% by weight of thepolymerizable unsaturated compound and/or solvent (D) based on the totalweight of the composition.